1. Field of the Invention
This invention relates to abrasive slurries, abrasive articles made employing the abrasive slurries, and to methods of making abrasive articles.
2. Background
In general, abrasive articles comprise a plurality of abrasive particles bonded either together (e.g., a bonded abrasive or grinding wheel) or to a backing (e.g., a coated abrasive). These abrasive articles have been utilized to abrade and finish workpieces for over a hundred years. One problem that has faced the abrasive industry is the generally inverse relationship associated between the cut rate (i.e., the amount of a workpiece removed for a given time interval) and the surface finish that is imparted by the abrasive article on the workpiece surface. This explains why there exists a wide range of abrasive products from coarse grit (i.e., relatively large particle size of abrasive particles) to fine grit (i.e., relatively small particle size of abrasive particles). Typically, these types of abrasive products are sequentially used in an abrading operation to achieve both the desired cut and the desired surface finish.
One solution to the problem described above is disclosed in U.S. Pat No. 5,152,917 (Pieper et al.). Pieper et al. disclose a structured abrasive article that provides both a high rate of cut and a consistent surface finish in the workpiece surface. The structured abrasive coating comprises abrasive composites that are bonded to a backing and that have a precise shape. Pieper et al. disclose that an abrasive article with a precise spacing of pyramidal shaped composites provides a high cut rate and fine surface finish. The abrasive composites of Pieper et al. comprise a plurality of abrasive particles dispersed in a binder.
A challenge in producing structured abrasive articles is to control the physical properties of the abrasive composites in order to provide an abrasive article which has both a long service life and a high rate of cut. When in use in an abrading operation, structured abrasive articles erode, that is, they gradually and controllably expose new abrasive particles to the workpiece being abraded. In order to provide an abrasive article with a long life and a high rate of cut, the rate of erosion of the abrasive composite must be controlled. If the rate of erosion is too high, the abrasive article will have a short useful life. If the rate of erosion is too low, the exposed abrasive particles will dull resulting in a low rate of cut.
The rate of erosion of a composite is affected, at least in part, by the size of the abrasive particles in the composite, and the distribution of abrasive particles throughout the composite. As larger abrasive particles are used (i.e., for coarser abrasive articles) the amount of binder holding the abrasive particles together in the abrasive composite is decreased. This results in a weaker abrasive composite, having a higher rate of erosion and shorter useful life. Additionally, if the abrasive slurry used to form the abrasive composite is not stable, the abrasive particles contained therein may not remain substantially uniformly distributed throughout the binder. This may result in an abrasive coating being formed which has a non-uniform distribution of binder and abrasive particles. Such an abrasive coating may have a high rate of erosion due, at least in part, to a high concentration of abrasive particles being present with inadequate binder to bond the particles together.
In view of the foregoing, it is desirable to produce an abrasive article which has both a high rate of cut, (i.e., such as would be provided by using larger sized abrasive particles), while maintaining a long useful life. Furthermore, it is desirable to produce an abrasive slurry in which the abrasive particles contained therein remain substantially uniformly dispersed for a reasonable period of time.